This research was conducted to design and build an application system for Child Disease Diagnosis Expert Systems using an Android-based platform and forward chaining method as an algorithm, to help parents to detect early illnesses in children and their handling information so as to reduce the risk of mishandling and also reduce fears and stress on parents is also a guide for doctors to treat patients. This application will provide information about various types of childhood diseases and early treatment of these diseases. The design and implementation of an Android-Based Child Disease Diagnosis Expert System is carried out by the Multimedia Laboratory of the Department of Electrical Engineering, Ujung Pandang State Polytechnic as well as a Field Study at the Hospital. Data Flow Diagrams (DFD) explain the flow of data in expert systems. Admin input data in the form of disease symptoms and rule data into the expert system. Then the data that has been entered into the expert system is used by the user to diagnose the disease through the input of symptoms experienced by the patient and the results are in the form of conclusions of the illness suffered by the patient. Use Case Diagrams are used to illustrate the functional requirements of the Android-Based Pediatric Diagnosis System Expert Application and how this application interacts with the user. Where, the visitor actor is a user who uses the system for consultation and finding information about the disease. Acting visitors can do activities to see about the disease, see about the application, see the guide, and login. If the login is successful the user is an admin actor or doctor actor. Admin actor can perform admin activities such as managing user data, managing symptom data, managing solution data and managing visitor data while the doctor or medical officer actor cannot manage user data. The output in this study is an application of Expert System for Diagnosing Children's Diseases using the Android Platform that can work in accordance with an algorithm that has been built and runs well by performing compatibility testing on several Android-based smartphones